In tissue-conserving surgery sequential layers of tissues are excised to ensure the removal of all tumour cells while maintaining as much healthy tissue as possible. Negative margins (in which all cancerous cells are removed) have been directly associated with lower local recurrence rates in many cancer types. Conservation of healthy tissue is important for tissue function preservation, wound healing and cosmesis. However, identifying the tumour margins intra-operatively remains one of the key challenges in tissue-conserving surgery.
Histopathology is generally considered to be the “gold standard” method for evaluation of tissues for many diseases, including cancer. This involves staining of thin tissue sections (thickness ˜10 μm) with various contrast enhancing chemicals followed by examination under an optical microscope, which allows the discrimination of tissue structures and identification of any tumours. Histopathology is an invaluable tool for evaluating the tumour resection margins during tissue-conserving surgery.
Mohs micrographic surgery (MMS) for the treatment of basal cell carcinoma (BCC) relies on the removal of sequential tissue layers, which are evaluated during surgery by frozen section histopathology. If the pathologic evaluation during MMS indicates tumour persistence, the location of the tumour is recorded and further tissue removal is performed by the surgeon. BCC is a major health problem as it accounts for ˜75% of skin cancer cases worldwide with more than 60,000 cases being diagnosed each year in the UK. Although BCC rarely spreads to distant sites in the body, these cancers can lead to significant tissue destruction and dysfunction. Some BCCs have higher risks of recurrence (43% for regions near the eye and 33% for superior orbital rim and brow), which lead to more aggressive recurrent BCCs. If the treatment option were selected based on lowest recurrence rate, it has been argued that MMS would be chosen for every BCC (Arch Dermatol 1999; 135(10): 1255; Brit J Dermatol 1999; 141(3): 415). It has been shown that the 5-year recurrence rates for BCC treated by MMS are 1.4%-2.5% for primary and 2.4%-4% for recurrent BCC, significantly lower than for standard excision (3.2%-10% for primary and 12.1%-17% for recurrent BCC). However, the high costs have limited the availability of MMS throughout the UK, leading to an inequitable health service provision. In 2006 NICE (the UK National Institute for Health and Clinical Excellence) recommended that every specialist skin cancer team should be equipped with MMS for treating BCC. This is not the case at present due to limited availability of histopathology technicians skilled in frozen section preparation and skilled surgeons. Failure to provide MMS for difficult cases of BCC results in additional surgery for removal of recurrent tumours, causing additional morbidity for BCC sufferers and deferred costs to the NHS.
In many cases, the traditional methods of histopathological examination of resection specimens require tissue preparation procedures which, for practical reasons, cannot be performed intra-operatively. For example, breast conserving surgery (BCS) relies on visual or X-ray inspection of excised tissues, techniques which have significantly lower diagnosis accuracy compared to histopathology. Breast cancer is the most common type of cancer for women (45,000 new patients per year in the UK) and approximately 58% of the patients have BCS as their first treatment option. However, a recent retrospective study showed that 20% of patients in England treated by BCS between 2005 & 2008 required a secondary surgery (The Lancet Oncology 2012, 13:e334). This study highlights the low accuracy of the current methods used for intra-operative diagnosis. Secondary surgery has numerous negative consequences, including delaying adjuvant treatment, poorer aesthetic outcomes, longer recovery times, emotional stress to patients and increased costs to the healthcare services. The increased healthcare costs associated with secondary surgery represents a huge challenge to the healthcare service, especially when considering the current plans in the UK to expand the screening program to women younger than 50. Such expansions will lead to an increased number of patients with early stage breast tumours, for whom BCS is generally the most appropriate treatment.
Recently, Raman spectroscopy has emerged as a powerful technique for the diagnosis of cancers and imaging of tumours. Raman hand-held probes based on fibre optics have already been proposed for intra-operative evaluation of tumour margins (PNAS 2005; 102(35): 12371) as well as for guided biopsy (Opt Lett 2009; 34(6): 758). However, these methods allow only single-point measurements, which lack the spatial accuracy to detect small tumours. Spectral imaging based on Raman microscopic techniques has the advantage of containing both the morphological and chemical information at a high spatial resolution suitable for the detection of small tumours.
Alterations in the molecular properties of tissues during tumour growth provide the additional quantifiable information which can be used for objective diagnosis. Raman microscopy techniques have been used for imaging tumours within thin tissue sections (10-20 μm thickness) and multivariate statistical models had been developed for providing accurate diagnosis (typical sensitivities and specificities higher than 95%) for a wide range of tissues, including skin (J Biomed Opt 2009; 14(5): 054031) and prostate (Bju Int 2010; 106(4): 484). While these studies demonstrated the potential for using Raman microscopy for both imaging and unsupervised diagnosis of tumours, the work reported so far used raster-scanning (or line-scanning), which limited the diagnosis to small tissue areas (below 1 mm) or only single point measurements. Measurements of larger tissue samples at the required spatial resolution of 10-15 μm would require 20-40 hours, which is not practical during surgery. Thus, these methods are not suitable for diagnosis of thick and large tissue samples (1-2 cm) as typically excised during tissue conserving surgery.
It is an object of the invention to address one or more of the above mentioned problems.